This invention relates generally to intraocular lenses, and, more particularly, to multi-part intraocular lenses that can be surgically implanted in an eye through an incision that is smaller than the diameter of the lens' optic.
In the human eye, the crystalline lens is situated behind the pupil and iris and it functions to focus light entrant through the cornea and pupil onto the retina at the rear of the eye. The lens is a biconvex, highly transparent structure made of slender, curved rod-shaped ectodermal cells in concentric lamellae surrounded by a thin capsule. The lens capsule is supported at its periphery by suspensory ligaments, called zonules, that are continuous with the ciliary muscle.
A cataract condition results when the material within the lens capsule becomes clouded, thereby obstructing the passage of light. To correct this condition, two forms of surgery are used. In intracapsular cataract extraction, the entire lens is removed intact. To accomplish this, the surgeon severs the zonules or suspensory ligaments about the entire periphery of the capsule, and removes the entire lens with the capsule and its content material intact.
In extracapsular cataract extraction, an incision is made through the front wall (i.e., the anterior capsule) of the lens, and the clouded cellular material within the capsule is removed through this opening. Various techniques are used to accomplish this removal. The transparent rear capsule wall (i.e., the posterior capsule), as well as the zonules and peripheral portions of the anterior capsule (i.e., the anterior capsule flaps), all remain in place in the eye.
Both intracapsular and extracapsular extraction eliminate the light blockage due to the cataract. However, the light now entrant through the cornea and pupil is unfocused since there is no longer a lens in the eye. Appropriate focusing can be achieved by a lens (i.e., a contact lens) exterior to the eye. This approach, though generally satisfactory, has the disadvantage that when the external contact lens is removed, the patient effectively has no useful sight. A preferred alternative is to implant an artificial, intraocular lens directly within the eye. The lens is implanted through an incision made near the periphery of the cornea.
The length of the incision in the eye is an important factor in determining the rate of healing following lens implantation. A longer incision usually means longer post-operative recovery and healing periods for the patient. Other problems associated with lengthy incisions include expulsive hemorrhage, iris prolapse, bleb formation and high astigmatism. Accordingly, it is desirable to reduce the length of the incision as much as possible.
There have been several efforts in the past to reduce incision length by specially configuring the intraocular lens. In one such effort, the lens includes separable elements that are inserted individually into the eye and then connected together using surgical tools. These separate lens elements may include portions of the lens body itself, as well as position-fixation haptics or loops projecting outwardly from the lens body to center the lens within the eye. Using this technique, it is possible for the incision length to be smaller than the final diameter of the lens body or optic.
Although the individual insertion of separable lens elements permits use of a smaller incision, it necessarily requires the use of surgical tools within the eye, to assemble the elements together. This increases the risk of accidentally touching and irreparably injuring the eye's cornea, iris or capsule. In addition, the necessity of separately inserting and connecting together a number of lens elements within the eye complicates an already delicate positioning procedure.
Another lens that can be implanted through an incision smaller than the final diameter of the lens body includes a central lens member and two side lens members hinged to opposite sides of the central member. The side members pivot about axes in the plane of the central member. In use, the lens members are folded together for insertion into the eye through a relatively small incision and are then unfolded using a suitable tool, to produce a generally circular lens. The unfolding of the lens elements within the eye risks accidentally touching and irreparably injuring the eye's cornea, iris and capsule.
Still another lens that can be implanted through an incision smaller than the final diameter of the lens body is constructed of a transparent material that is highly flexible, such as silicone. Such lenses are folded for insertion through a small incision, and then unfolded into their final shape within the eye. Again, the unfolding within the eye risks injury to the cornea, iris and capsule. In addition, it is preferred to use harder and less flexible lens materials such as polymethyl methacrylate, which have been used successfully for decades.
It should therefore be appreciated that there has existed a definite need for an intraocular lens capable of being inserted into an eye through an incision having a length smaller than the lens' diameter, without increasing the risk of accidental eye injury and without requiring the use of highly flexible materials such as silicone. The present invention fulfills this need.